Rayfront User Manual

Metal Material Types

The metal, metal2, metfunc and metdata materials are for opaque surfaces, where specular highlights are modified with the material color. A pattern modifying the metal material types will affect the material color.

Metal

Metal is the simplest metallic material type.

Color:
The color values will modify the diffusely and specularly reflected light.

[0.0 0.0 0.0]

black (full absorption)

[1.0 1.0 1.0]

white/mirror (no absorption)

Values lower than [0.01 0.01 0.01] or higher than [0.95 0.95 0.95] are rare.

Specularity:
The fraction of incident light that is immediately reflected in mirror like fashion.

0.5

dirty

1.0

clean mirror

Roughness:
Roughness is specified as the rms slope of surface facets. A value of 0 corresponds to a perfectly smooth surface, and a value of 1 would be a very rough surface. Roughness values above 0.2 are unusual. The roughness affects only the specular reflection.

0.0

polished

0.5

roughened

Metal2

Metal2 is similar to metal, but with anisotropic roughness. This means that specular highlights in the surface will appear elliptical rather than round.

Roughness u:
Roughness v:
The roughness is specified seperately along the direction of the anisotropy (u) and along the direction on the surface perpendicular to it (v). Both values can't be smaller than 0.001. The highlight will be narrower in the direction of the smaller roughness value.


The vector u is defined on the Procedural page of the dialog.

Function File:
This pop-up list offers all function files known to the system for selection. If a file is active, then the variables in that file can be selected for one or several of the vector coordinates. Otherwise, the coordinates must be entered as expressions. Edit...
Start the text editor that was configured in the project preferences to edit the function file. New...
Create a new function file, and start the text editor to edit it.

Direction Vector X/Y/Z:
The coordinates of the direction vector orienting the anisotropy can either be selected from the variables in a function file as selected above, or they may be entered as expressions. An expression can contain numeric values, operators and all functions and variables known to the material. If an expression is not valid, then the entry field will have a red background, and the message bar at the bottom of the dialog will show a diagnostic message.

The Transformation page of the dialog can be used to transform the vector, possibly to bring it in alignment with the geometry of the surface the material modifies.

Metfunc

The metfunc material type is for opaque surfaces with arbitrary bidirectional reflectance distribution functions (BRDF) and has the same basic properties as metal, with the exception of roughness. Roughness isn't required here, since the BRDF specification is much more powerful.

Function File:
This pop-up list offers all function files known to the system for selection. Edit...
Start the text editor that was configured in the project preferences to edit the function file. New...
Create a new function file, and start the text editor to edit it.

Reflection Function:
An arbitrary bidirectional reflectance distribution function (BRDF) defined in the function file above. The function takes four arguments, the x, y and z direction towards the incident light and the solid angle subtended by the source (which is supplied to faciliate averaging, but is often ignored). Radiance will also accept functions with less parameters. The pop-up list offers all formally valid functions from the function file for selection.
The selected function should integrate to 1 over the projected hemisphere.

Real Arguments
Rayfront will check the selected function file to decide how many real arguments the material definition should supply. If this number is greater than the mandatory arguments specifying the basic properties, then the expected number of entry fields in the list is made available. Supplying those arguments is optional, but failing to do so may result in runtime errors when the selected function relies on a specific argument which is not set.

The Transformation page of the dialog can be used to transform the vector, possibly to bring it in alignment with the geometry of the surface the material modifies.

Metdata

The metdata material type is used for arbitrary BRDFs that are most conveniently given as interpolated data and has the same basic properties as metal, with the exception of roughness. Roughness isn't required here, since the BRDF specification is much more powerful.

Function File:
This pop-up list offers all function files known to the system for selection. Edit...
Start the text editor that was configured in the project preferences to edit the function file. New...
Create a new function file, and start the text editor to edit it.

BRTD Function:
An arbitrary bidirectional reflectance distribution function. The function takes five arguments, the interpolated data value, the x, y and z direction towards the incident light and the solid angle subtended by the source (which is supplied to faciliate averaging, but is often ignored). Radiance will also accept functions with less parameters. The pop-up list will offer all formally valid functions from the function file for selection.
The selected function should integrate to 1 over the projected hemisphere.

Data File:
The file containing the reflectance data for interpolation. Rayfront currently limits valid data to three dimensions.
Import...
This button invokes a file open dialog, and the selected data file will then be imported into the project.

Index Functions:
One or several functions (depending on the number of dimensions in the data file) to index into the data. The functions take four arguments each, the x, y, and z coordinates of the direction to the incident light and the solid angle subtended by the light source. Functions with less arguments are also valid.

Real Arguments
Rayfront will check the selected function file to decide how many real arguments the material definition should supply. If this number is greater than the mandatory arguments specifying the basic properties, then the right number of entry fields in the list is made available. Supplying some or all of those arguments is optional, but failing to do so may result in runtime errors when the selected function relies on a certain argument, and this argument is not specified.

The Transformation page of the dialog can be used to transform the vector, possibly to bring it in alignment with the geometry of the surface the material modifies.

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